1. Field of the Invention
This invention relates to a process for producing acrylic fibers having non-circular cross-sections by wet-spinning an inorganic solvent solution of an acrylonitrile polymer through a spinnerette having circular spinning orifices. More particularly, the invention relates to a process for producing acrylic fibers having non-circular cross-sections which are excellent in gloss, softness, etc., in which process a particular acrylonitrile polymer solution is spun and coagulated, and the resulting filaments are washed with water and stretched in wet heat, these process steps being carried out in integral combination and under specific conditions.
2. Description of the Prior Art
The processes for producing acrylic fibers are classified broadly into wet-spinning methods and dry-spinning methods, and in each of these methods, fibers of characteristic features are produced. In respect of touch feel such as softness, slipperiness, etc., the fibers produced by the latter method are better by the reason of their fiber cross-sectional shape such as cocoon shape or heart shape, and the smoothness of the fiber surface. In wet-spinning method, especially that using an inorganic solvent, the speed of solvent removal at the time of coagulation is slow and the coagulation occurs uniformly throughout the outer and inner layers of the fiber, so that fibers with circular cross-sections are liable to be formed, and in addition, because of numerous wrinkles formed on the fiber surface, the fibers do not necessarily have the so-called animal hair-like touch and are not satisfactory in gloss, softness, slipperiness, etc.
Heretofore, much effort has been directed to the attainment of processes of providing fibers having non-circular cross-sections by wet-spinning method using an inorganic solvent. All of these processes have not been satisfactory from an industrial viewpoint. For example, as described in Japanese Patent Publication No. 2328/1970, satisfactory fibers having non-circular cross-sections can be obtained by using a plastic-made spinnerette having non-circular orifices, but this process involves an industrial problem in that the productivity is low because the spinnerette has a low pressure resistance. Also, a method was proposed wherein fibers extruded through a metallic spinnerette having circular orifices located near to each other, are agglutinated and united to form fibers with non-circular cross-sections. In this method, however, there is an unevenness in agglutination between the peripheral and central parts of the spinnerette, so that there are different cross-sectional shapes and also fibers of non-united, circular cross-sections are present in mixture.